docs: def new_file(self, path, track_idx, copy_file=False):
          """
          Adds a new audio file to the corpus with the given data.
  
          Parameters:
              path (str): Path of the file to add.
              track_idx (str): The id to associate the file-track with.
              copy_file (bool): If True the file is copied to the data set folder, otherwise the given
                                path is used directly.
  
          Returns:
              FileTrack: The newly added file.
          """
  
          new_file_idx = track_idx
          new_file_path = os.path.abspath(path)
  
          # Add index to idx if already existing
          if new_file_idx in self._tracks.keys():
              new_file_idx = naming.index_name_if_in_list(new_file_idx, self._tracks.keys())
  
          # Copy file to default file dir
          if copy_file:
              if not os.path.isdir(self.path):
                  raise ValueError('To copy file the dataset needs to have a path.')
  
              __, ext = os.path.splitext(path)
  
              new_file_folder = os.path.join(self.path, DEFAULT_FILE_SUBDIR)
              new_file_path = os.path.join(new_file_folder, '{}{}'.format(new_file_idx, ext))
              os.makedirs(new_file_folder, exist_ok=True)
              shutil.copy(path, new_file_path)
  
          # Create file obj
          new_file = tracks.FileTrack(new_file_idx, new_file_path)
          self._tracks[new_file_idx] = new_file
  
          return new_file